Lextacy09

Hey there everyone. I'm hoping someone can really help me. I'm having an issue with my SC400 and I have literally tried everything to fix it. My issue is this... After about 20 minutes of run time, I start idling rough, it starts as a light sputtering in the exhaust, and then it gets really bad. I'm able to accelerate just fine, but when I get between 40-50mph, it seems as if it's misfiring, and car starts shaking hard. But once I get past 50, smooth sailing. Now to the interesting part, I have no CEL (of course) and this is what I've already replaced...

1.) TPS
2.) MAF
3.) IACV
4.) Spark Plugs (Laser Iridium)
5.) Wires
6.) BOTH Distributor Caps and Rotors
7.) BOTH sub o2 sensors (behind the cats)
8.) I've also pulled the entire exhaust manifold and cleaned it out (twice with Carb cleaner)
9.) BOTH Ignition Coils
10.) Cleaned the EGR valve twice
11.) Replaced all Gaskets between manifold and surrounding areas

I'm at my wits end everyone. I've tried everything. And the only place I can even take my car to that charges a reasonable amount of money can't look at it until next week. ANY HELP OR GUIDANCE IS SO GREATLY APPRECIATED!!! THANKS SO MUCH!!!

Tabaka

iTrader: (8)

Your symptoms happened to someone I knew. They had a bad ECU and everything was perfect afterwords. What year is your car? It might be time for a ECU replacement or capacitor repair. Open up your ECU and look inside. Just my 0.02 cents.

1WILLY1

iTrader: (9)

yea if u did all that try the ecu next,

also check your cam and crank sensors, i had one loose before it took 3 mechanics and a few weeks to diagnose

jadu

iTrader: (42)

I concur with the ecu. It's strange how things go south after 20 minutes. moving to maintenance

SC400slide

iTrader: (11)

Either the engine ECU, or the fuel pump ECU.

Lextacy09

Thanks everyone, I rally appreciate it...

And Tabaka, its a 1992, 210,800 miles...
Hopefully I can snag a good ECU for relatively good price...

Clean400

iTrader: (2)

Try the fuel pump ecu bypass before you buy anything.